Methods and systems for detecting and characterizing cell-types, both in terms of the number of a particular cell-type and the type of single cellular organism, as well as the cell's phenotype are needed. Methods and instruments that can rapidly identify cell-types and numbers of a particular cell-type in a biological sample could be useful in medical diagnosis, food monitoring, and environmental sampling.
Current methods of identifying cells include the use of PCR techniques, antibodies, and various culture conditions. For example, current methods of identifying bacterial cells include culturing the cells in a desired medium. Such techniques are often time consuming and inadequate. For example, there must be some a priori knowledge of what biological species are being cultured in order to provide the correct growth medium; growing a colony may also take up to a day and consume expendibles, one must subsequently dispose of the cultured colony to avoid hazard to the environment. This disposal process itself constitutes a risk to the environment.
Several techniques are currently proposed or in development at other laboratories for microbial detection. These include UV fluorescence, UV resonance Raman spectroscopy, and the use of optimal DNA probes for simultaneous capture, amplification, and fluorescence-detection of several bacterial types. While the UV fluorescence and resonance-Raman methods are conceptually simple, they appear to have limited specificity and sensitivity. The UV fluorescence spectra of many bacteria are similar and hence one must appeal to pattern-recognition algorithms for identifying the quantifying microorganisms at the aggregate, genus, and species level. The data processing requires a high signal-to-background in the spectra, thus relatively high organism densities (103-104 colony forming units (CFUs) in the field of view of the excitation source), resulting in limited sensitivity, in addition to a reduced probability of detection (the detector system must be rastered over a large field of view in order to chance upon the micro-organism). Similar effects arise in UV resonance Raman spectroscopy. Raman signatures and shifts can also depend on bacterial culture conditions and age, thus impeding identification. Another approach involves DNA amplification, which has excellent selectivity and parallel detection of several bacterial types. Without incubation, the sensitivity of DNA amplification is about 10 CFUs.
Accordingly, conventional techniques require long incubation times, costly consumables and skilled technical knowledge and labor. A rapid sensitive method of typing cells in a biological sample may be useful in the medical field where current laboratory techniques, even when performed at their most rapid pace, provide results that are 8-12 hours old.